1. Field of the Invention
The present invention relates to a keyboard apparatus having plural keys, and more particularly to a keyboard apparatus having electronic actuators that apply a reaction force with respect to the operation of depressing the plural keys.
2. Description of the Related Art
A natural keyboard instrument such as an acoustic piano or the like is configured to generate a live sound by a hammer, which rotates with the key depression, striking a string, for example. The natural keyboard apparatus of this type has a so-called action mechanism provided between a key, which is a performance operation element, and a hammer. A player receives a unique reaction force (key damping force) from the key by this action mechanism. Specifically, a feeling of a key touch specific to the natural keyboard instrument can be obtained by providing the action mechanism.
On the other hand, in a conventional electronic keyboard instrument, such as an electronic piano, that generates an electronic sound, a mechanical structure, such as a spring or a mass body (hammer) member, that returns a key to an initial position is provided in order to simulate a touch feeling of a natural keyboard apparatus such as an acoustic piano. A player operates a key against the returning force of the spring or the mass body member when he/she depresses the key. In general, the mechanical structure of the electronic keyboard apparatus is compact and not complicated, compared to the action mechanism of the natural keyboard apparatus, so that the touch feeling of a key in the electronic keyboard apparatus is different from the touch feeling of the natural keyboard apparatus, to be strict.
In view of this, there has been proposed a keyboard apparatus in which a key is driven by driving means, such as an electromagnetic solenoid, for changing the reaction force against the key depression, in order to provide a touch feeling similar to that of a natural keyboard instrument in an electronic keyboard instrument. In the keyboard apparatus using the electromagnetic solenoid, a plunger (movable member) of the electromagnetic solenoid, which linearly moves in the vertical direction, and a key that pivots about a support should be engaged with each other so as to be capable of transmitting power. As a keyboard apparatus in which the plunger and the key is engaged with each other, there has been proposed a keyboard apparatus in which a groove is formed along the longitudinal direction of the key, and the leading end of the plunger is fitted into the groove so as to be slidable in the longitudinal direction (see Japanese Examined Patent Application No. HEI7-111631). However, in the conventional keyboard apparatus described above, the engagement structure is complicated, and a friction caused by the sliding movement is generated. Further, the conventional keyboard apparatus also entails a problem that looseness is produced between the groove formed to the key and the leading end of the plunger, which affects a feeling of a touch when the key is depressed.
As a keyboard apparatus that suppresses the looseness at the contact point of the key and the plunger to the minimum level, there has been proposed a keyboard apparatus including a key-depression-direction biasing member that biases the key in the key-depressing direction, and a key-release-direction biasing member that biases the key toward the key-release direction, and balances the key at a rest position in cooperation with the key-depression-direction biasing member (see Japanese Unexamined Patent Application No. HEI10-20857). It is to be noted that the rest position is the position where the biasing force of the key-depression-direction biasing member and the biasing force of the key-release-direction biasing member are balanced. However, in the conventional keyboard apparatus described above, the balance between the key-depression-direction biasing member and the key-release-direction biasing member affects the feeling of a touch upon the key depression. Therefore, the key-depression-direction biasing member and the key-release-direction biasing member should correctly be adjusted in order to balance the key at the rest position. The problem is that the adjustment described above is extremely difficult.